The purpose of this web site is to present an unbiased evaluation of the results of various medical studies which are published almost every day and compare these with relavent paper from the past few years. Often the results of these studies are incorrect, misinterpreted or exaggerated by medical scientist and by the news media. Hopefully, the information in this web site will help to clarify such problems and take the fear out of the many scary medical conclusions.

Tuesday, December 21, 2010

WHAT IS THE TRUTH ABOUT FAT AND DEATH

One day you read in the paper or hear on TV that being overweight will cause you to die earlier. The following week you hear just the opposite. So what should you believe? Well, it is not easy unless you read the original epidemiological literature and analyze the results yourself.

But, you don’t have to do that because I have already done it.

Recently I posted a blog concerning body weight and death in which I summarized two recent studies which showed that bodyweight and death were related by a U-shaped curve (shown below). That is, if you are too skinny or too fat (obese) you are at a greater risk of death and that just being overweight did not increase the risk.

As you can see, if you weight too much or too little your risk of death is increased by approximately 1 to 2 percent as compared with the normal weight people. The group numbers indicate bodyweight category: 1. Underweight, 2-4. Normal weight, 5-7 Overweight and 8-10 Obese. These data are for men but the data for women are very similar.

It is clear from these data that people in the overweight groups of 5-7 are not at any greater risk of death than the normal weight groups 3-4. But there is a greater risk for being underweight (groups 1 and 2) or obese (groups 9 and 10).

NEW STUDY

Now a new study says that both overweight and obese people are at greater risk of death (de Gonzalez et al 2010 N Engl J Med 363 2211). So what should you believe?

As noted above, in the field of epidemiology, which is where all of these kinds of studies come from, disagreement almost always exists. In the case of bodyweight and death the disagreement level is greater than usual and downright ridiculous. For example:

• AT LEAST 4 STUDIES HAVE PROPOSED THAT THERE IS NO DISTINCT RELATION.

• OTHERS HAVE PROPOSED THAT THE RELATIONSHIP IS J-SHAPED (7 STUDIES)

• SEVEN STUDIES SAY THE CURVE IS U-SHAPED AS I DESCRIBED IN MY PREVIOUS BLOG

• AND 6 STUDIES SAY THE RELATIONSKIP IS LINEAR AND 4 SAY ITS INVERSELY LINEAR

So if the data and conclusions are so contradictory why go on? Why not just accept that the fact that the truth about fat and death will never be clear? Because very recently a paper was published which claims it has uncovered the truth and all other studies should be ignored (de Gonzalez et al 2010 N Engl J Med 363 2211). Right off the bat you realize, it can’t be true, so what is the real story.

This group has combined a large study which made up of 57 other studies (Prospective Studies Collaboration 2009 Lancet 373 1083) and added four more in order to come up with their own set of data from which they conclude that being overweight or obese will cause you to kick off sooner.

However, The Prospective Study showed the same U-shaped curve as we have already discussed. The only difference is that more groups were added in the Obese Category which made the curve slightly J-shaped. The values for Normal Weight average 9.6/yearly deaths /1000 and 9.8/yearly deaths/1000 for the Overweight group. Clearly not different. Hence being overweight poses no addition risk of death. The real skinny and obese groups were at a greater risk of early death but the overweight were not.

The deGonzalez group has taken the above data and combined it with four other studies and the combination was analyzed. Of the four studies listed two had no useable data and the other two are discussed below.

One of these by Hu et al (2004 N Engl J Med 351 2694) shows a linear trend of increase risk of death as a function of body mass index.

This is an example of an upward linear relationship and does not agree with most other studies. However the inclusion of these data in the de Gonzalez study decreases the upward curve of the underweight people and makes it appear that if there is a risk in this group it is very low. Notice that the difference between normal weight (2-3) and overweight (4-6) is 0.51-0.34= 0.17% which is not significant.

The study by Baik et al (2000 Am J Epidemiol 152 264) indicates that underweight people are at somewhat greater risk of death and that normal weight and overweight people are have no significant increase in risk. Whereas obese people are at somewhat greater risk.

Curiously, the study by Klenk et al (2009 Eur J Epidemiol 24 83) was not added to the list. Could it be because the data in Klenk et al 2009 show a U-shaped curve with conclusions about overweight people similar to those discussed above and obtained from McGee 2005 and Adams 2006.

In their final analysis de Gonzalez et al conclude that overweight and obese people are at greater risk of death. However, the small differences between overweight and normal groups are very small and of no biological significance. The authors are able to claim statistical significance because the number of subjects is so large. Thus many studies (some good, some poor, and some bad) many of which are not statistically significant can be brought together and suddenly statistical significance pops out. It is my opinion and the opinion of many others that such lumping of diverse studies into one analysis is a crock of statistical crap.

Obviously I believe that the U-shaped curve holds and overweight people are not at any greater risk of death than normal weight people.

About Me

I am retired professor who has painted off and on for much of my life. Until I retired I never had enough time to devote to art. However, since then I have figured out how to make famous paintings into dioramas. To my knowledge this has not been done before and I hope you like them.
I have another blog which reflects my interest in sex hormone research and other topics of interest in the clinical and epidemiological fields.
http://medicalmisssteps.blogspot.com